Process for the production of a braking band of a brake disk with ventilation ducts and a braking band produced by this process

ABSTRACT

A process for the production of a braking band having ventilation ducts comprises the steps of a) moulding a core of metallic material, b) inserting the core in a mould, in a central position, c) filling the mould with at least two layers of material which are to form the braking band, in a manner such that the core is “sandwiched” between the at least two layers, d) performing a first heating of the mould to a temperature such as to bring about hardening of the at least two layers until the at least two layers adopt a three-dimensional structure, e) subjecting the semi-finished product produced in step d) to a second heating to a temperature such as to bring about fusion of the metallic material of the core, and f) collecting the molten core.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for the production ofa braking band of a brake disk with ventilation ducts and to a brakingband produced by this process.

[0002] In particular, the present invention relates to a process for theproduction of a braking band having ventilation ducts and made of aceramic material such as, for example, C/SiC.

[0003] The ventilation ducts of braking bands which are currentlycommercially available are generally produced by various methods.

[0004] A first method provides for the moulding of the braking band as asolid body and the subsequent formation of radial and non-radial holeslying in the central plane of the thickness of the band and constitutingthe ventilation ducts.

[0005] A second method for the production of braking bands of ceramicmaterial for a brake disk with ventilation ducts provides, in a firststep, for the separate moulding of two reflectively symmetrical portionsof the braking band, which have channels within their respectivesurfaces that face one another. The two portions are then brought intocontact and joined together to form the finished band in which thechannels of each of the portions together define the ventilation ducts.

[0006] In a third method, the ventilation ducts are produced by means ofa core of ceramic material which is inserted in the mould, between twolayers of the material for forming the band, and which already has inits interior the cavities which will constitute the ventilation ducts.Since it is made of material identical or at least similar to that ofthe band, the core becomes closely connected to the ceramic material ofthe braking band, forming a ceramic “sandwich” structure therewith. Thecore itself is formed by two half-cores arranged facing one another andjoined together in a similar manner to that described for the brakingband of the above-mentioned second production method.

[0007] However, the above-mentioned methods have some problems anddisadvantages connected mainly with technological difficulties.

[0008] In the first method, the formation of the holes in the thicknessof the braking bands is in fact very expensive and difficult because ofthe hardness of the materials used. Moreover, the machining inside thebraking band is much less controllable than the external machining ofthe band. During this machining, it is consequently not possible toexclude the formation of sharp edges or even cracks, which cannot betolerated in the production of a braking band.

[0009] The second method, on the other hand, has the disadvantage of theneed to join together two portions of a braking band which, since theyare moulded separately, may not correspond and may therefore fittogether unevenly. This could give rise to a product in which dangerousdetachment of these two portions due to non-symmetrical forces caneasily occur.

[0010] With regard to the third method, this requires the provision oftwo moulds for the moulding of the respective half-cores, as well as athird mould for the moulding of the braking band. Moreover, in order toachieve satisfactory results, the core produced by means of the twohalf-cores has to be positioned very accurately inside the mould formoulding the braking band. All of this requires quite complex techniquesas well as manual intervention in every moulding cycle. Theabove-mentioned technological complexities, as well as the resultingcosts, also reduce the competitiveness of brake disks of ceramicmaterial with ventilation ducts, in comparison with non-ventilateddisks.

[0011] There is consequently a need to provide a process for theproduction of braking bands with ventilation ducts which is particularlyeasy to implement and economical.

SUMMARY OF THE INVENTION

[0012] The problem underlying the present invention is therefore that ofproviding a process for the production of braking bands which hascharacteristics such as to satisfy the above-mentioned needs and, at thesame time, to overcome the disadvantages of the methods of the priorart.

[0013] This problem is solved by a process for the production of abraking band as defined in the appended method claims.

[0014] A second subject of the present invention is a metal core forforming cavities within a ceramic material, as defined in the appendedproduct claims.

[0015] A third subject of the present invention is a braking band whichcan be produced by the process of the present invention, as defined inthe appended product claims.

[0016] The Applicant of the present invention has in fact selected aparticular material for the formation of the core and particulartemperature ranges in which the material which is to form the brakingband hardens, adopting a three-dimensional structure, and in which thematerial of a core “sandwiched” between the layers which are to form thebraking band melts. This enables a braking band provided withventilation ducts produced in the void left by the melted core to beproduced more simply and economically than those of the prior art.

[0017] The expression “three-dimensional structure”, referring to thematerial which is to form the braking band of the present invention, isintended to mean that the material has a configuration such as not tocollapse on itself at the temperature at which the core starts to melt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further characteristics and the advantages of the process for theproduction of braking bands, as well as braking bands produced by theprocess according to the present invention will become clear from thefollowing description of some preferred embodiments thereof, given byway of non-limiting example, with reference to the appended drawings, inwhich:

[0019]FIG. 1 is a schematic, perspective view of the core by means ofwhich the ventilation ducts of the braking band according to theinvention are produced,

[0020]FIG. 2 is a view showing, in section, a mould in the operativestage for the moulding of the braking band according to the invention,

[0021]FIG. 3 is a perspective view of the braking band according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] As shown in FIG. 1, the core 100 is formed by an outer peripheralring known as the core support 100 a and by an inner peripheral ring112, which are connected to one another by connecting elements 111 bymeans of which the ventilation ducts of the braking band are produced.

[0023] The inner peripheral ring 112 has projecting portions 113 whichextend for a predetermined distance towards the core support 100 a. Inparticular the projecting portions 113 are such as to form correspondingseats for housing the teeth of a brake-disk bell.

[0024] The connecting elements 111 by means oL which the ventilationducts of the braking band are produced, may also be arranged atirregular intervals and may be inclined to one another.

[0025] Moreover, the connecting elements 111 may have many differentshapes such as, for example, shapes which impart to the ventilationducts 11 of the braking band substantially circular or prismaticcross-sections.

[0026] The core 100 is made of metal and is produced in a conventionalmould.

[0027] Typical examples of these moulds are a die-casting mould orpermanent moulds.

[0028] The core 100 is preferably made of a metal alloy which can meltat a temperature of between 150 and 450° C.

[0029] Preferred examples of these metal alloys are those selected fromthe group comprising tin-based and zinc-based alloys.

[0030] Examples of these tin-based alloys are Sn—Pb and Sn—In alloys.Preferably, they are the Sn—Pb alloy having 37% w/w of Pb and the Sn—Inalloys having from 10 to 20% w/w of In, in particular, the Sn—In alloyhaving 15% w/w of In, at the eutectic. Even more preferably, thetin-based alloy is the Sn—Pb alloy having 37% w/w of Pb at the eutectic.

[0031] An example of a suitable zinc-based alloy is Zn—Al alloy.Preferably, it is the Zn—Al alloy having 4% w/w of Al.

[0032] According to one embodiment of the present invention, when themetal core 100 is a tin-based alloy, it can melt at a temperature ofbetween 150 and 250° C., preferably between 180 and 220° C.

[0033] According to a further embodiment of the present invention, whenthe metal core 100 is a zinc-based alloy, it can melt at a temperatureof between 250 and 450° C., preferably between 300 and 400° C.

[0034] The above-mentioned core of metallic material can therefore beused to form a cavity inside any body of ceramic material such as, forexample, C/SiC.

[0035] In order to mould the braking band according to the presentinvention, the core 100 is inserted in a suitable mould.

[0036] This step of the moulding of the braking band will now bedescribed with reference to FIG. 2.

[0037]FIG. 2 shows schematically the mould, generally indicated 101.

[0038] The mould 101 comprises two plates 300 and 400 which, inoperative conditions, are coupled so as to define a moulding cavity 500.

[0039] Two opposed pistons 600 and 700 are mounted inside the mouldingcavity 500 and can slide along a common axis X-X. The pistons 600 and700 are constructed in a manner such as to seal against the internalwalls of the moulding cavity 500.

[0040] In particular, the mould 101 has housings 800 for housing thecore support 10 a of the core 100, between the two pistons 600, 700.

[0041] The step of the moulding of the braking band with the use of theabove-mentioned mould will now be described below, with reference toFIG. 2.

[0042] Initially, when the mould 101 is in the open configuration (notshown), that is, when the two plates 300 and 400 with the respectivepistons 600 and 700 are spaced apart, a layer 900 of a mixture in thesolid state is deposited in the moulding cavity 500.

[0043] Typically, the solid-state mixture of the layer 900 comprisesfibres and/or filaments of carbon-based materials selected from thegroup consisting of fibrous materials produced by pyrolysis of variousproducts of synthetic origin, for example, polyacrylonitrile (PAN) andpolysilazane, or of natural origin, for example, pitches, naturalcellulose-based sources, such as vegetable fibres and wood.

[0044] These materials are mixed with a binder such as, for example, aphenolic resin, an acrylic resin, a paraffin, pitches, and polystyrenes.

[0045] The binder is preferably selected from the group comprisingpitches and phenolic resins.

[0046] The binder may be added to the mixture in any desired form, forexample, in the solid, semi-liquid, or liquid state, or in solution.

[0047] For example, the phenolic resin may be added in the form ofpellets, powder, or granules.

[0048] The content of organic binder in the mixture may vary from 5% to30% by volume, relative to the volume of the mixture, and is preferablywithin the range of 20%-26%.

[0049] The mixture may also contain further conventional additives usedas fillers and, indirectly, for regulating the porosity and the densityof the desired composite material.

[0050] These additives are constituted by particles of inorganicmaterials such as, preferably, powders of graphite, silicon carbide, ormetal carbides or nitrides.

[0051] The content of additives in the mixture may vary from 0.7% to 23%by volume, relative to the volume of the mixture, and is preferablywithin the range of 9%-15%.

[0052] As shown in FIG. 2, the layer 900 is deposited on the surface 701of the piston 700 which faces the piston 600 of the plate 300.

[0053] The core 100 is then positioned on top of the layer 900 so as tocover it and, at the same time, in a manner such as to be kept suspendedand not to sink into the mixture. This suspension is achieved by meansof the core support 10 a of the core 100.

[0054] After the core 100 has been positioned in the moulding cavity500, a further layer 901 of the above-mentioned mixture is deposited ontop of the core 100 so as to produce a layered arrangement.

[0055] At this point, the mould 101 can be closed so that the lowersurface 601 of the piston 600 comes into contact with the layer 901.

[0056] The braking band is moulded by a first heating stage, to atemperature and at a pressure exerted by the pistons 600 and 700 on thelayers of mixture 900 and 901, which are such as to bring abouthardening of the layers 900 and 901 until they adopt a three-dimensionalstructure.

[0057] Typically, this first heating stage is performed at a temperatureof between 80 and 180° C. and at a pressure of between 0.1 and 5 N/cm².Advantageously, the first heating stage is performed at a temperature ofapproximately 150° C. and at a pressure of approximately 1 N/cm².

[0058] The semi-finished product thus produced is then removed from theappropriate mould and placed in a conventional furnace.

[0059] In the furnace, the semi-finished product is subjected to asecond heating stage, to a temperature such as to melt the core 100.Once molten, the metallic material constituting the core 100 iscollected in a crucible for reuse.

[0060] Advantageously, no cooling is performed between the first andsecond heating stages.

[0061] The second heating stage is performed at a temperature whichdepends substantially on the type of metal of which the core 100 isformed.

[0062] As stated above, for a core 100 of tin-based alloy, thetemperature of the second heating stage is preferably between 150 and250° C., even more preferably between 180 and 220° C., whereas, if thecore 100 is a zinc-based alloy, the temperature of the second heatingstage is preferably between 250 and 450° C., even more preferablybetween 300 and 400° C.

[0063] The above-mentioned second heating stage leads to a semi-finishedproduct comprising ventilation ducts in the empty space left by thedischarge of the molten core 100.

[0064] In a preferred embodiment of the present invention, the first andsecond heating stages are performed in a single mould.

[0065] Upon completion of the second heating stage, the semi-finishedproduct may be treated in accordance with the prior art in theproduction of braking bands.

[0066] Typical examples of these treatments are pyrolysis andsilication. They are preferably performed as described in theApplicant's European patent application No. 00830093.1 which is includedherein by reference insofar as it relates to the above-mentionedpyrolysis and silication treatments in which pyrolysis takes place at atemperature of between 900 and 1200° C. and in the presence of a streamof inert gas such as nitrogen and argon and with an extra pressure of10-100 mbar and the silication is performed at a temperature of1400-1700° C. under vacuum, reducing the pressure from 900 mbar to 300mbar.

[0067] Moreover, if necessary, the braking band according to theinvention thus produced may be subjected to finishing operations, forexample, surface finishing which may be performed dry or wet, inconventional manner, by means of a grinding operation.

[0068] Moreover, it is known that, in some cases, braking bands made ofthe materials described above may give rise to possible cracks orfractures as a result of thermal and/or compression stresses to which abraking band is subjected during use. These cracks or fractures tend topropagate rapidly throughout the structure of a braking band and maycause it to disintegrate completely.

[0069] Advantageously, a plurality of reinforcing fibres may beintroduced into the mixture for the moulding of the braking banddescribed above to impede the propagation of cracks.

[0070] Examples of these reinforcing fibres and of their incorporationin the mixture which is to form the braking band are described in theApplicant's European patent application No. 00830093.1 which is includedherein by reference insofar as it relates to the above-mentionedreinforcing fibres and their incorporation.

[0071]FIG. 3 shows a braking band 10 containing internal ventilationducts (not shown) in the empty space left by the discharge of the moltencore 100.

[0072] The braking band 10 also has an outer peripheral edge 10 a havingopenings 11 a corresponding to the ventilation ducts described above andan inner peripheral edge 12 provided with seats 13 such as to housecorresponding teeth of a bell of a brake disk (not shown).

[0073] The advantages of the process for the production of the brakingband of the present invention are clear from the foregoing.

[0074] A first advantage is that the core, by means of which theventilation ducts of the braking band of the present invention areproduced, is made of a material that can start to melt at a temperatureat which the material that is to form the braking band has alreadyadopted a three-dimensional structure. This enables the ventilationducts to be formed without causing the collapse of the braking bandbeing moulded on the core.

[0075] A second advantage is that the core is made of a material whichhas good flow characteristics. The steps of the filling of the mould andof the collection of the material of the molten core are thusfacilitated. Moreover, this prevents residues of the material whichforms the core remaining attached to the braking band which is beingmoulded.

[0076] A third advantage is that the process for the production of abraking band according to the invention is inexpensive to implement.

[0077] A fourth advantage of the process is that it can be carried outin a single mould. This permits a further reduction in costs.

[0078] In addition, the presence of the core support 100 a provides asuitable support for the core and, at the same time, achieves optimalbalancing of the pressures exerted by the two pistons 600 and 700 duringthe step of the moulding of the braking band.

[0079] The present invention is thus realized by the provision of asimple and economical process that can also produce a braking band whichhas the necessary safety characteristics from the structural point ofview, and which is easy to produce.

[0080] Naturally, in order to satisfy contingent and specificrequirements, a person skilled in the art may apply to theabove-described process and to the braking band many modifications andvariations all of which, however, are included in the scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A process for the production of a braking bandhaving ventilation ducts, comprising the steps of: a) moulding a core ofmetallic material, b) inserting the core in a mould, in a centralposition, c) filling the mould with at least two layers of materialwhich are to form the braking band, in a manner such that the core is“sandwiched” between the at least two layers, d) performing a firstheating of the mould to a temperature such as to bring about hardeningof the at least two layers until the at least two layers adopt athree-dimensional structure, e) subjecting the semi-finished productproduced in step d) to a second heating to a temperature such as tobring about fusion of the metallic material of the core, and f)collecting the molten core.
 2. A process according to claim 1 in whichthe core is a metal alloy which can melt at a temperature of between 150and 450° C.
 3. A process according to claim 2 in which the core ofmetallic material is an alloy selected from the group comprisingtin-based alloys and zinc-based alloys.
 4. A process according to claim3 in which the tin-based alloys are Sn—Pb and Sn—In alloys.
 5. A processaccording to claim 4 in which the tin-based alloys are Sn—Pb alloyshaving 37% w/w of Pb and Sn—In alloys having from 10 to 20% w/w of In,at the eutectic.
 6. A process according to claim 5 in which thetin-based alloy is the Sn—Pb alloy having 37% w/w at the eutectic.
 7. Aprocess according to claim 6 in which the alloy is Sn—Pb having 37% ofPb at the eutectic.
 8. A method according to claim 3 in which thezinc-based alloy is Zn—Al alloy.
 9. A process according to claim 8 inwhich the zinc-based alloy is the Zn—Al alloy having 4% w/w of Al.
 10. Aprocess according to claim 1 in which, in step d), the first heating isperformed at a temperature of between 80 and 180° C. and at a pressureof between 0.1 and 5 N/cm².
 11. A process according to claim 10 in whichthe first heating is performed at a temperature of approximately 150° C.and a pressure of approximately 1 N/cm².
 12. A process according toclaim 1 in which, in step e), the second heating is performed at atemperature of between 150 and 450° C.
 13. A process according to claim12 in which the core is a tin-based alloy and the second heating isperformed at a temperature of between 150 and 250° C.
 14. A processaccording to claim 13 in which the second heating is performed at atemperature of between 180 and 220° C.
 15. A process according to claim12, in which the core is a zinc-based alloy and the second heating isperformed at a temperature of between 250 and 450° C.
 16. A processaccording to claim 15 in which the second heating is performed at atemperature of between 300 and 400° C.
 17. A process according to claim1 in which step f) is followed by a step of reuse of the molten metallicmaterial constituting the core.
 18. A core of metallic material forforming a cavity within a body of ceramic material, wherein it is atin-based alloy as described in claim
 4. 19. A core of metallic materialfor forming a cavity within a body of ceramic material, wherein it is azinc-based alloy as described in claim
 8. 20. A braking band which canbe produced by the method described in preceding claim
 1. 21. A core ofmetallic material for forming a cavity within a body of ceramicmaterial, wherein it is a tin-based alloy as described in claim
 13. 22.A core of metallic material for forming a cavity within a body ofceramic material, wherein it is a zinc-based alloy as described in claim15.
 23. A braking band which can be produced by the method described inpreceding claim 17.